Pancreatic Lipoma: MRI Findings

Pancreatic mesenchymal tumors account for 1-2% of all pancreatic tumors. The pancreas is a very rare location for fat-containing tumors. Few cases of pancreatic lipomas has been reported in the imaging literature. Lipomas are usually asymptomatic, detected incidentally and appear as a discrete, well encapsulated fat attenuation mass within the pancreatic parenchyma. Imaging features of pancreatic lipoma are diagnostic and doesn’t need histopathological evidence as long as patients are asymptomatic and follow benign course. The density measurements on CT images consistent with fat are virtually diagnostic. Typical CT findings are hypodensity (from -30 to -120 HU) and homogeneity, with no significant contrast enhancement and without infiltration of peripancreatic fat. Lipomas appear as hyperechoic on ultrasound with posterior acoustic attenuation, with some instances of hypoechogenicity. MRI is extremely helpful in showing presence or absence of macroscopic fat. On T1-weighted images, mature adipose tissue demonstrates high signal intensity and signal drop on fat suppressed sequence, while a T2-weighted image shows variable signal intensity with no enhancement on contrast images. Differential diagnosis include focal fatty infiltration of the pancreas, teratoma (mature dermoid cyst), and liposarcoma. Patients with pancreatic lipomas have no associated risk factors such as prior history of pancreatitis, alcoholic hepatitis, obesity, diabetes mellitus etc. They are distinctive in terms of their boundaries; contain collagen capsule around and no signs of malignancy. Rapid enlargement > 5 cm may need histological confirmation to rule out liposarcoma. Surgical intervention is done if there are any signs of ductal or vessel obstruction and hemorrhage. Overall the prognosis is excellent.